Magnetic Random Access Memory (xe2x80x9cMRAMxe2x80x9d) is a non-volatile memory that is being considered for short-term and long-term data storage. MRAM has lower power consumption than short-term memory such as DRAM, SRAM and Flash memory. MRAM can perform read and write operations much faster (by orders of magnitude) than conventional long-term storage devices such as hard drives. In addition, MRAM is more compact and consumes less power than hard drives. MRAM is also being considered for embedded applications such as extremely fast processors and network appliances.
A typical MRAM device includes an array of memory cells, word lines extending along rows of the memory cells, and bit lines extending along columns of the memory cells. Each memory cell is located at a cross point of a word line and a bit line.
The memory cells may be based on tunneling magneto-resistive (TMR) devices such as spin dependent tunneling (SDT) junctions. A typical SDT junction includes a pinned layer, a sense layer and an insulating tunnel barrier sandwiched between the pinned and sense layers. The pinned layer has a magnetization orientation that is fixed so as not to rotate in the presence of an applied magnetic field in a range of interest. The sense layer has a magnetization that can be oriented in either of two directions: the same direction as the pinned layer magnetization, or the opposite direction of the pinned layer magnetization. If the magnetizations of the pinned and sense layers are in the same direction, the orientation of the SDT junction is said to be xe2x80x9cparallel.xe2x80x9d If the magnetizations of the pinned and sense layers are in opposite directions, the orientation of the SDT junction is said to be xe2x80x9canti-parallel.xe2x80x9d These two stable orientations, parallel and anti-parallel, may correspond to logic values of xe2x80x980xe2x80x99 and xe2x80x981.xe2x80x99
The magnetization orientation of the pinned layer may be fixed by an underlying antiferromagnetic (AF) pinning layer. The AF pinning layer provides a large exchange field, which holds the magnetization of the pinned layer in one direction. Underlying the AF layer are usually first and second seed layers. The first seed layer allows the second seed layer to be grown with a (111) crystal structure orientation. The second seed layer establishes a (111) crystal structure orientation for the AF pinning layer.
FIG. 1 is an illustration of a magnetic memory device according to an embodiment of the present invention.
FIGS. 1a and 1b are illustrations of different magnetization orientations of the magnetic memory device.
FIG. 2 is an illustration of hysteresis loops for data and reference layers of the magnetic memory device.
FIG. 3 is an illustration of a write operation on the magnetic memory device.
FIGS. 4a-4f are illustrations of read operations on the magnetic memory device according to embodiments of the present invention.
FIG. 5 is an illustration of an MRAM device according to an embodiment of the present invention.
FIGS. 6a, 6b and 6c are illustrations of methods for reading an MRAM device according to embodiments of the present invention.
FIG. 7 is an illustration of an exemplary method of fabricating an MRAM device.
FIGS. 8-11 are illustrations of a clad conductor according to a first embodiment of the present invention, the clad conductor shown during different stages of fabrication.
FIG. 12 is an illustration of a clad conductor according to a second embodiment of the present invention.